1. Field of the Invention
This invention relates to a temperature-sensitive indicator which indicates irreversibly that a temperature has risen to a prescribed temperature or higher or has fallen to a prescribed temperature or lower, and in particular relates to a temperature-sensitive indicator that visually enables to confirm exposure to an environment at a prescribed temperature or higher, or at a prescribed temperature or lower.
2. Description of the Related Art
In recent years, temperature management has become important in management of merchandise and products. For example, when handling perishable foods, cut flowers and other perishable items, pharmaceuticals, or semiconductor materials, if products are exposed to temperatures at or above a prescribed temperature without performing adequate temperature management, the quality of the merchandise or product may decline, or there may be degradation, or propagation of bacteria, or spoiling.
Hence strict temperature management of such merchandise and products is necessary not only at the time of production, but during physical distribution and storage as well; and temperature-sensitive indicators are used as one means of continuously monitoring such temperature management.
As such temperature-sensitive indicators, that described in Japanese Examined Patent Application Publication H3-562 (Patent Reference 1) has been proposed. The temperature-sensitive indicator described in Patent Reference 1 is explained based on FIG. 11 and FIG. 12. In the figures, the symbol 51 is a base, and on the upper face of this base 1 is arranged a wall portion 51a which has a ring shape in planar view. Further, on the upper face of the base 51 on the inside of this wall portion 51a is provided a porous pad 52. This porous pad 52 is saturated with a solution of a dye and a chemical material which remains in the solid phase at and below a critical temperature, but at or above the critical temperature changes to the liquid phase.
On the upper-end face of the wall portion 51a is mounted a display core 53. And, the top of the display core 53, and the outer peripheral face of the wall portion 51a, are covered by a cap 54. This cap 54 has a convex shape and is formed into a so-called dome, such that when a certain external force acts, the center portions is collapsed and deformed into a concave shape. The display core 53 is enclosed between this cap 54 and the wall portion 51a, and hold the display core 53. In addition, an adhesive 55 is formed on the rear face of the base 51, and a release liner 56 is provided so as to cover this adhesive 55.
The release liner 56 is peeled from the temperature-sensitive indicator 50 configured in this way, the base 51 is affixed to merchandise or a product, and then, the center portion of the cap 54 is pressed in with a finger to bring the display core 53 into contact with the porous pad 52.
When the product or similar onto which this temperature-sensitive indicator 50 is affixed is exposed to a prescribed temperature or above, the dye in the porous pad 52 changes from the solid to the liquid phase, and due to the concentration gradient between the display core 53 and the porous pad 52, the colored chemical material moves from the porous pad 52 to the display core 53. As a result, by visibly confirming the colored state of the display core 53, it is possible to judge whether the product or similar has been exposed, even once, to an environment at or above a prescribed temperature.
However, with such a temperature-sensitive indicator there are concerns that upon storage in a high-temperature environment the dye may change to the liquid phase and then evaporate, or that the chemical substance solution may evaporate, and so there has been the problem that when storing such temperature-sensitive indicators, temperature management of the temperature of the temperature-sensitive indicator itself is necessary. Moreover, when the center portion of the cap 54 is pressed in with a finger, there is the problem that the temperature of the finger is sensed.
Further, another temperature-sensitive indicator is proposed in Unexamined Utility Model Application Publication No. 57-29829 (Patent Reference 2).This temperature-sensitive indicator is explained based on FIG. 13 and FIG. 14.
In the figures, the temperature-sensitive indicator 60 comprises a base 61; capsules 62, provided on the base 61, into which is packed a mixture of an oil-soluble coloring agent, pigment or dye, mixed with a solid material comprising a straight-chain hydrocarbon or with a composition comprising a straight-chain hydrocarbon (a so-called colored wax); and, filter paper 63, provided so as to cover the capsule 62.
When using this temperature-sensitive indicator 60, a finger is used to exert pressure onto the capsules 61 from above the filter paper 63, to crush the capsules 62. When the temperature rises to a prescribed temperature or higher, the colored wax melts, and the oil-soluble coloring agent, pigment or dye permeates the filter paper. Hence by visibly confirming the coloration state of the filter paper 62, it is possible to judge whether the product or similar has been exposed, even once, to an environment at or above a prescribed temperature.
In this temperature-sensitive indicator 60 described in Patent Reference 2, the so-called colored wax, which is an oil-soluable coloring agent, pigment, or dye mixed with a solid material comprising a straight-chain hydrocarbon or with a composition comprising a straight-chain hydrocarbon, because the so-called colored wax is housed within capsules, evaporation can be suppressed, and management at normal temperatures is possible.
However, a temperature-sensitive indicator such as that described in Patent Reference 1 which judges whether there has been exposure to an environment at or above a prescribed temperature has the problem that, when pressing in the center portion of the cap with a finger, the finger temperature is detected. Similarly, a temperature-sensitive indicator such as that described in Patent Reference 2 has the problem that, when a finger is used to press on and rupture capsules, the so-called colored wax packed inside the capsules is liquefied by the temperature of the finger, so that when capsules are ruptured the filter paper assumes a colored state, and use is no longer possible.
Moreover, the capsules are merely placed on the flat base, so that when the capsules are pressed with the finger, capsules elude the pressing force, and so there is the problem that capsules are not ruptured.